This invention relates to compositions having an improved flame resistance and based on thermoplastic polymers, selected in particular from amongst olefinic polymers and polystyrene, or based on polymeric compositions utilized in the production of paints.
Such polymers are particularly sensitive to the ignition with flame, wherefore they need a suitable protection especially for the applications, in which the probability of a breaking out of fire is rather high.
Various methods of reducing the inflammability of the polymers are known from the art.
One of these methods consists in adding to the polymer an organic substance, partially chlorinated or brominated, and therefore thermally unstable, preferably in combination with compounds of antimony, tin or arsenic. Such combinations are rather efficient in imparting the desired flame resisting properties to the polymers, but have the drawback of being to be used in rather high concentrations in order to give a satisfactory result, this leading to a worsening of the mechanical properties of the polymers which said combinations are added to.
Furthermore these combinations exhibit the drawback of a strong evolvement of toxic fumes and gases in case of fire, besides that of causing the corrosion of the equipment in which the polymeric materials containing them are processed.
Other methods consist in adding to the polymers easily decomposable substances, with simultaneous evolvement of incombustible gases, such as ammonium phosphates or hydrated alumina.
Recently the research has been directed towards antiflame additives consisting of combinations of an ammonium phosphate or of another organic phosphorus containing compound and of one or more organic substances capable of giving, by thermal decomposition, uninflammable gaseous products (water, carbon dioxide, ammonia, nitrogen) and carbonaceous residues.
Among the various useful phosphorus containing compounds the preferred ones are, because more easy to be found, the ammonium polyphosphates falling within the general formula: EQU (NH.sub.4).sub.n+2 P.sub.n O.sub.3n+1
in which n is an integer equal to or higher than 2; preferably the polyphosphates' molecular weight must be high enough as to assure a low water-solubility.
The composition of the polyphosphates having the above formula, in which n is a sufficiently high number (higher than 20), is practically the one corresponding to the formula of metaphosphates (NH.sub.4 PO.sub.3).sub.n.
Some examples of such polyphosphates are "Exolit 263" (manufactured and sold by Benckiser Knapsak GmbH.) having the composition (NH.sub.4 PO.sub.3).sub.n, in which n is higher than 50, and "Phos-Chek P/30" (manufactured and sold by Monsanto Chemical Co.) having a similar composition.
Other employable phosphates are those deriving from amines, such as dimethylammonium and diethylammonium phosphate, ethylenediamine phosphate, melamine ortho- or pyrophosphate and still other phosphates.
Some compounds that, by thermal decomposition, provide gaseous products and carbonaceous residues are, for example, the polyalcohols, such as glycerol, trimethylol-ethane, trimethylol-propane, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,6-hexane-triol, the carbohydrates in general (starch, cellulose, sugars) and nitrogen containing compounds, such as melamine, cyanuric acid, urea, thiourea, dicyandiamide, benzoguanamine and derivatives and condensation products thereof.